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Calculating the load current and load voltage

  1. Feb 11, 2014 #1
    1. The problem statement, all variables and given/known data

    Attached.

    2. Relevant equations



    3. The attempt at a solution

    Attached.

    For #2, how do I get VL and IL?
     

    Attached Files:

  2. jcsd
  3. Feb 11, 2014 #2

    gneill

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    Staff: Mentor

    For #2 you are to assume that ##V_L## is a given, along with ##V_{th}## and ##R_{th}##.
     
  4. Feb 11, 2014 #3
    By a given, you mean I just leave them as variables instead of giving them values, right?
     
  5. Feb 11, 2014 #4

    gneill

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    Well, the Thevenin voltage and resistance should have numerical values that you calculated previously, but the ##V_L## is a new independent variable. You want to find an expression for ##I_L(V_L)##.
     
  6. Feb 11, 2014 #5
    Would the below be correct?

    I used mesh analysis.

    $${ I }_{ L }=\frac { { V }_{ th }-{ V }_{ L } }{ { R }_{ th } }$$
     
  7. Feb 11, 2014 #6

    gneill

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    Exactly like that :smile:
     
  8. Feb 11, 2014 #7
    For #4, I calculated IL, VL, and PL for RL=2200 ohms but I'm not sure how to get power transfer efficiency.

    $$I_{ L }=1.745\cdot 10^{ -3 }A\\ V_{ L }=3.838V\\ P_{ L }=6.70\cdot 10^{ -3 }W$$
     
  9. Feb 11, 2014 #8

    gneill

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    Your power value looks a bit off, probably rounding/truncation error sneaking into your significant figures. Try keeping a few more decimal places in intermediate steps.

    I'm not sure how they want you to define power transfer efficiency for this problem. Does your text give any examples?

    Usually this sort of exercise would be leading up to a discussion of the Maximum Power Transfer Theorem. See if your text describes it; it may show you their definition of power transfer efficiency.
     
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